Dispersive effects in laser ablation plasmas

Abstract

The dynamics of transient plasmas generated by high-fluence nanosecond laser ablation has been investigated by recording the ionic current with a Langmuir probe. Systematic measurements have been carried out on a plasma produced in vacuum by Nd:YAG laser irradiation of a copper target. The temporal evolution of the ionic current for different fluences was investigated, revealing the presence of some periodic oscillations. A theoretical model is proposed in order to describe the nonlinear behavior of the expanding plasma by assuming that the motion curves of the ablated particles are fractals. The behaviors predicted by the proposed theoretical model are in good agreement with the experimental findings.

Lorenz Type Behaviors in the Dynamics of Laser Produced Plasma

“…One of the most important results is the prediction and confirmation of ionic oscillations by using invasive techniques. The oscillatory behavior coupled with heterogenic dynamics of different ions is well in line with the image depicted by other groups [20,33] and by our group in past papers [5,13,31]. In this paper the oscillatory behavior and the double layer-like distribution appear as natural solutions to the initial paradigm which translated the initial complex Lorenz system from laser to target to plasma.…”

“…In the past few years, three other theoretical approaches where proposed. One based on the fractal model developed as the interaction between two fractal structures [5,31], and their corresponding interface (generally, this interface delineates the double layer), with the second ones being on differential physics [28]: a collisional model based on the plasma ion frequency and electron-ion collision rate in the context of the Lieberman's model for plasma immersion ion implantation, and finally, one based on the AC Josephson effect. So, at this point there is no real consensus for the real mechanism behind the oscillatory behavior but intense theoretical and experimental work is undergoing to shed some light on it.…”

Charged Particle Oscillations in Transient Plasmas Generated by Nanosecond Laser Ablation on Mg Target

“…Their nature is often debated with some reports presenting their roots in the dynamics of a plasma structure generated by electrostatic mechanisms [24], or induced by the transient double layers generated through plasma structuring [25]. Other novel theoretical approaches have been presented either in the framework of a fractal theoretical model [12,26] or built around Lorenz-type systems [27]. The complete behavior of plasma charged particles can be accounted for in the framework of the aforementioned fractal paradigm with the oscillatory behavior being explained through the presence of dissipative [12] or dispersive [26] effects, and the classical behavior is better showcased in the compact fractal hydrodynamic model [28].…”

“…Other novel theoretical approaches have been presented either in the framework of a fractal theoretical model [12,26] or built around Lorenz-type systems [27]. The complete behavior of plasma charged particles can be accounted for in the framework of the aforementioned fractal paradigm with the oscillatory behavior being explained through the presence of dissipative [12] or dispersive [26] effects, and the classical behavior is better showcased in the compact fractal hydrodynamic model [28]. The fractal paradigm proposes that every dynamic variable describing laser ablation plasma systems acts as the limit of families of functions.…”

Investigations of Laser Produced Plasmas Generated by Laser Ablation on Geomaterials. Experimental and Theoretical Aspects

“…Since in these conditions the non-differentiability (fractality) appears as a fundamental property of the ablation plasma dynamics it seems necessary to construct a corresponding non-differentiable plasma physics model, for example in the form of fractal hydrodynamics model [46]. The mathematics behind this model as well as some applications of the model were development in a systematic manner by our group in [28,29,46,47]. In the following, a fractal analysis will prove a multi-structuring of the ablation plasma in the form of Coulomb, thermal and cluster structures.…”